In a third generation partnership project LTE (3GPP LTE) system, a mobile terminal can use a physical uplink shared channel (PUSCH) to report a channel quality indicator (CQI) non-periodically. The non-periodical report consists of three kinds of mode: a wideband mode, a mobile terminal selection mode and a high-level configuration mode; and a high level configures which mode can be used semi-statically.
During reporting the CQI, the mobile terminal needs to report a combined index related to subband indexes of M subbands selected by itself firstly. When the CQI is reported through the mobile terminal selection mode, it is defined:
      〈                            x                                      y                      〉    =      {                                                      (                                                                    x                                                                                        y                                                              )                        ,                                                x            ≥            y                                                            0            ,                                                              x              <              y                        ,                              where
  (                                   x                                      y                      )  represents a combination number extracting y elements from x different elements,
            (                                    x                                                y                              )        =                  x        !                              y          !                ⁢                              (                          x              -              y                        )                    !                      ;
the mobile terminal reports a combined index
  r  =            ∑              i        =        0                    M        -        1              ⁢                         〈                                                            N                -                                  s                  i                                                                                                        M                -                i                                                    〉            to an Evolved Node B (eNB), wherein N represents the number of subbands of a downlink system, and M represents the number of subbands selected by the mobile terminal; and a set {si}i=0M−1 comprising M subband indexes sorted in ascending order, i.e., subband indexes of M subbands, wherein 1≦si≦N, and si<si+1.
At present, the subband index can be determined by the combined index with reference to a direct table lookup method, which specifically is:
an eNB obtains possible values of M and N according to a formula N=downlink system bandwidth/subband size as well as a correspondence table of downlink system bandwidth, subband size and M; calculates all possible values of r and each value of si corresponding to different values of r according to definition above and the possible values of M and N; generates and stores a lookup table comprising each possible value of each r and {si}i=0M−1 corresponding to that each possible value according to the result of the calculation; after receiving a r reported by the mobile terminal, the eNB inquires the stored lookup table to obtain {si}i=0M−1 corresponding to the received r, that is, the subband indexes of M subbands, wherein the correspondence table of downlink system bandwidth, subband size and the number of the subbands that can be selected by the mobile terminal is shown in Table 1.
Wherein the possible values of r are within a range from 0 to
      (                  (                                            N                                                          M                                      )            -      1        )    ,and each possible value of r corresponds to {si}i=0M−1, it can be seen that there is a great amount of data contained in the lookup table. Therefore, when the direct table lookup method is used to determine a subband index, a large storage space is needed for storing a lookup table, which cause an increase in the hardware cost of the eNB.
TABLE 1Downlink systemSubbandThe number of subbands that canbandwidthsizebe selected by a mobile terminal6-7NANA 8-102111-262327-6335 64-11046